This article contains information that relates to the non-canon game Pikmin: Ultimate Doom by Wraith.
The Basement is the first cave players may enter in Pikmin: Ultimate Doom. It is not a regular cave, and as such is called an Event Cave. There are no enemies in this cave, just a cutscene that encompasses most of the time here. However, there are multiple hazards in this cave.
This is the only floor, and consequently the final floor. It is a rather open space with mists flowing all around. When Louie sets foot into this cave, the dozens of bunches of scattered vines start to whip around, grabbing Louie's Red Pikmin and him also. His armor glowing blue, he struggles but manages to break free. His Pikmin all fall to the floor, their respective vines having caught on fire. The vines scatter and flap around, putting the fire out. Then the vines retract into the ground just before a massive tremor shakes Louie off of his feet. His Pikmin are unaffected by this tremor, and form a circle around a shadow. Then the Red Onion drops through the ceiling and slams to the ground, kicking up dust and dirt. Louie, trying to see through the dirt, dust, and fog, wipes his visor, just barely feeling its crack, which increased in size by a little. He lifts a boulder and throws it to the side, hitting a cluster of vines. The vines move around to near Louie and stop. Then the player can order the Pikmin to attack it, and they all tap their leaves on it. The vines all retract into the ground, confusing Louie. But then he sees a red glow where the vines used to be. He approaches to only see none other than Olimar! His suit is stuck in a cycling state, and so he is also knocked out cold. Louie lifts Olimar up and grabs onto the leg of the Onion, while the Pikmin get into it. Then it lifts up out of the cave, flying over to the landing site and landing near the Trailblazer.